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Title: Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning systems for rift valley fever virus

Author
item TCHOUASSI, DAVID - University Of Pretoria
item SANG, ROSEMARY - University Of Pretoria
item SOLE, CATHERINE - Centers For Disease Control - Kenya
item BASTOS, ARMANDA - Centers For Disease Control - Kenya
item Teal, Peter
item BORGEMEISTER, CHRISTIAN - International Centre Of Insect Physiology And Ecology
item TORTO, BALDWYN - Centers For Disease Control - Kenya

Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2012
Publication Date: 1/10/2013
Citation: Tchouassi, D.P., Sang, R., Sole, C.L., Bastos, A.D., Teal, P.E., Borgemeister, C., Torto, B. 2013. Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning systems for rift valley fever virus. PLOS Neglected Tropical Diseases. 7(1):1-11.

Interpretive Summary: Rift Valley fever, a mosquito-borne zoonosis, is a major public health problem in sub-Saharan Africa and has considerable potential for spread throughout the world. This threat is exacerbated by important key gaps in our knowledge of RVF that limit an efficient early warning and response systems. Surveillance to monitor mosquito populations during the periods of low mosquito prevalence and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. However, current mosquito surveillance programs which rely on the CO2-baited CDC light trapping system are inadequate to meet these challenges due to its low sensitivity, non-specificity and trapping of a wide range of non-target insects. Scientists in the Chemistry Research Unit CMAVE-USDA-ARS, Gainesville, FL in collaboration with scientists at the International Center for Insect Physiology and Ecology, Nairobi, Kenya, Department of Zoology and Entomology, University of Pretoria, South Africa, and Center for Chemical Ecology, Department of Entomology, Pennsylvania State University, University Park, PA have been studying host attraction of mosquito vectors of Rift Valley Fever. They identified a series of host produced aldehydes that when released from monitoring traps are far superior in attracting vector mosquitoes than is any currently available monitoring system. The sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVF mosquito vectors especially during the periods when populations of the vectors are low.

Technical Abstract: Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health problem in sub-Saharan Africa. The emergence and re-emergence of the disease in the last 20 years especially in East Africa, poses a looming health threat which is likely to spread to beyond Africa. This threat is exacerbated by important key gaps in our knowledge of RVF that limit an efficient early warning and response systems, particularly an understanding of the distribution and dynamics of the virus among vectors and hosts between epidemics. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. However, current mosquito surveillance programs which rely on the CO2-baited CDC light trapping system is inadequate to meet these challenges due to its low sensitivity, non-specificity and trapping of a wide range of non-target insects. The alternative surveillance technique of using living animal hosts of RVF poses increasingly ethical challenges. Here, we report a more sensitive and mosquito-specific surveillance trapping system for RVF vectors based on mammalian-skin derived semiochemicals. In field bioassays in Marigat and Ijara districts, two hotspot areas of the disease in Kenya, we demonstrated that skin volatiles from known RVF mammalian hosts (cow, donkey, goat, sheep and human) combined with CO2-baited CDC lightless trap serve as potent kairomones for mosquito RVF vectors. Using a combination of field bioassays, electrophysiological and chemical analyses, we further demonstrate that skin-derived aldehydes are common to these hosts, and they serve as potent attractants for these mosquito vectors of the disease. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVF mosquito vectors especially during the IEP.